Surface hardening of titanium



United States Patent SURFACE HARDENING OF TITANIUM Charles W.. Vigor, Detroit, Mich., assignor to General Motors Corporation, Detroit, Mich., a corporatlon'of Delaware No Drawing. Application February 19, 1954 .Serial No. 411,561

Claims. (Cl. 29-198) um and then heat treating the materials at a temperature below the melting point of the titanium and the powdered metal and also below any eutectic temperature of the titanium and the powdered metal to cause diffusion of the metals.

Suitable powdered metals which I have found may be successfully employed are nickel, manganese, chromium,

etc. Under some conditions mixtures of these metals also may be used. The metal powders either may be pure or may be the commercial grades of nickel, manganese and chromium. Powdered binary alloys of nickel and manganese, nickel and chromium, and chromium and manganese and ternary alloys of nickel, manganese and chromium also may be employed in place of the single metal powders. In these alloy powders, any proportion of the individual metals making up the alloy powders is suitable.

If desired, more than a single diffusion layer may be formed. For example, the diffusion treatment may be carried out by first applying a powdered metal and diffusing the same and thereafter applying another layer of powdered metal and subjecting the previously treated article to a further diffusion treatment. The second layer of powder may be the same as the first or it may be a different metal, mixture of metals, or an alloy of the metals.

It is important that the titanium and metal powder be maintained free of oxides. Accordingly a neutral atmosphere is employed during the diffusion heat treatment. Very pure argon is preferably used because it is heavier than air and hence may be conveniently employed to purge the furnace. Under some conditions helium or hydrogen may be employed in place of argon, or together with argon. The diffusion heat treatment also may be carried out in a vacuum.

In general it is preferred that the particle size of the powdered metal should be such that substantially all of it will pass through a 300 mesh screen. However, under some conditions coarser powders between 100 and 300 mesh may be used.

Best results are obtained when the powdered metal is mixed with a liquid organic vehicle and the mixture applied to the titanium or titanium alloy. The organic vehicle should be of a composition which will readily volatilize or decompose into non-toxic. and non-irritating gaseous substances when exposed to the temperatures employed in the diffusing treatment. The vehicle should leavenoiash or residue after decomposition at high temperatures. Examples of such materials are the glycolic compounds such as ethylene glycol, diethylene glycol, propyleneglycol or the like, lacquers, and liquid polymeric compounds such as liquid Lucite.

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The following are specific examples of procedure in accordance with the invention:

Example 1 A titanium panel was first cleaned and then had applied thereto a thin layer of a mixture of volatile lacquer and fine nickel powder. The titanium panel and the nickel powder thereon were then heat treated in'an argon atmosphere for three hours at 1700 F. to cause diffusion of the metals. This temperature is below the melting points of both nickel and titanium and also below any nickel-titanium eutectic temperature. At the end of this time the treated panel was subjected to metallographic examination and the results showed a solid-solid diffusion of nickel and titanium hadtaken place to a depth of .015 inch. This alloy layer was found to have a maximum hardness of 310 DPH in the as diffused condition ascompared to a hardness of 180 DPH for the titanium panel itself. Upon heating the diffused panel at 1700 F. and quenching in water a maximum hardness of 480 DPH was observed. Subsequent tempering at 800 F. for onehalf hour lowered the maximum hardness to 360 DPH. The nickel powder employed was such that substantially all of it would pass through a 300 mesh screen. In general it is contemplated that temperatures of approximately 1410 F. to 1750 F. may be employed for the diffusion heat treatment in usingnickel powder. The time of the diffusion heat treatment is somewhat dependent on the temperature employed and in general the time of diffusion heat treatment may range from about one-fourth hour to about ten hours.

Example-2 In place of nickel powder as in Example 1 another titanium panel was treated by applying a thin layer of manganese powder (300 mesh or finer) in a volatile lacquer and heat treated at a temperature of 1850 F. in a pure argon atmosphere for three hours to cause diffusion of the metals. The diffusion layer had a maximum as-difiused hardness of 370 DPH ascompared to a hardness of 180 DPH for the titanium panel. Reheating to 1700 F. and water quenching gave a maximum hardness of 410 DPH. Tempering one-half hour at 500 F. increased the maximum hardness to 620 DPH. In general a temperature of 1000 F. to 2200 F. may be employed where manganese forms the surface material, the lower temperatures necessitating longer times of dilfusion and A thin layer of a mixture of chromium powder and a liquid organic vehicle was applied to a titanium panel and thereafter heat treated at 1850 F. for three hours in an argon atmosphere. At the end of this time a hardness test indicated the treated surface was increased in hardness, although to a lesser extent than in the case of Examples 1 and 2. In general a temperature of about 1300 F. to about 2550 F. may be employed where chromium forms the surface material. The time of the difiusion heat treatment is somewhat dependent on the temperature employed and in general the time may. range from about one-quarter hour to about ten hours.

Although titanium basealloys in general may be employed in the present invention, excellent results are obtained when a commercially pure metal is used. An example of a commercially available titanium alloy is one composed of approximately 0.1% iron, 0.08% tungsten, 0.02% nitrogen, carbon not in excess of 0.04%, a trace of oxygen,'and the balance substantially all titanium. Commercial titanium base alloys containing chromium, usually between 1.5% and 3%, may likewise be used. Thus an alloy composed of about 2.7% chromium, approxi- Patented Nov. 4, 1958 3. mately 1.3% iron, 0.25% oxygen, 0.02% nitrogen, tungsten not in excess of 0.04%, 0.02% carbon, and the balance titanium has proved to be satisfactory. Commercially available alloys may also be obtained with manganese contents as high as 7%and aluminum contents up to 5%. Y i i As used in the several claims titanium is intended to include not only pure titanium and commercial titanium but also titanium base alloys.

"While thepr esent invention has been described by means of certain specific examples, itwill be understood that the invention is not to be limited thereby. Various modifieations' and changes may be madeby those skilled in th'eart without departing from the principles and spirit offthef invention and I do not intend to limit the patent granted thereon except as necessitated by the prior art.

1.- ,A method of forming a surface layer on a titanium member which comprises applyingthereto a thin layer of at least one metal powder selected a from the group consisting of nickel, manganese and chromium and alloys thereof, and thereafter heatingthe titanium member and metalpowder to a temperature below the melting point of titanium and the powdered metal and below any eutectic-temperature of titanium and the powdered metal for a time 'suflicient to cause diffusion of the metal powder into the surface of said titanium member.

2. A irnethod of forming a hard surface layer on a titanium member which comprises applying thereto a mixture of an organic vehicle and at least one metal powder selected from the group consisting of nickel, manganese and chromium and alloys thereof, and thereafter heating the titanium member and metal powder to a temperat'ure below the melting point of titanium and the powdered metal and below'any eutectic temperature of the titanium and powdered rnetalin an inert atmosphere for a time sufficient to cause-diffusion of the metal powder into the surface of said titanium member.

3; A method'of forfning a hard surface layer on a titanium member which comprises applying thereto a mixture of an organic'vehiclea'nd at least one metal powder selected from the group consisting of nickel, manganese and chromium and alloys thereof,- and thereafter heating the titanium member and metal powder to a temperature below the melting point of titanium and the powdered metal and below any eutectic temperature of the titanium and powdered metal in an inert atmosphere of the class consistingof argon, helium, and hydrogen and mixtures.

thereof fora time within the range of about one-quarter hour'to about ten hours to cause diffusion of the metal powder into the surface of said titanium member.

4; A method of forming a hard surface layer on a titanium member which comprises applying thereto a mixture of an organic vehicle and at least one metal powder selected from the group consisting of nickel, manganese and chromium and alloys thereof, and thereafter heating the titanium member and metal powder to a temperature belowithe, melting point of titanium and the powdered metal and b elowa'ny eutectic temperature of the titanium and powdered metal in a vacuum for a time within the range of about one-quarter hour to about ten hours to cause diffusion of the metal powder into the surface of said'titanium member. j

5. A method of forming a hard surface layer on a titanium member which comprises applying thereto a mixture of a volatile organic vehicle and nickel powder, and thereafter heating the titanium and nickel in an inert atmosphere at a ter'nperaturejwithin the range of about 1410 F'. to 1750 F. for a time within the range of about one-"quarter hour to about ten hours to cause diffusion of the "nickel into the surface of said titanium member.

6. A method of forming ahard-surfacelayer on a titanium member which comprisesapplying thereto a mixture of a'jolatile organic v ehicleand manganese powder, and

thereafter heating the titanium and manganese in an inert atmosphere at a temperature within the range of about 1000 F. to 2200 F. for a time within the range of about one-quarter hour to about ten hours to cause diffusion of the manganese into the surface of said titanium member.

7. A method of forming a hard surface layer on a titanium member which comprises applying thereto a mixture of a volatile organic vehicle and manganese powder, and thereafter heating the titanium and manganese in an argon atmosphere at a temperature of about 1850 F. for a time of about three hours to cause diffusion of the manganese into the surface of said titanium member.

8. A method of forming a hard surface layer on a titanium member which comprises applying thereto a mixture of a volatile organic vehicle and chromium powder, and thereafter heating the titanium and chromium in an inert atmosphere at a temperature within the range of about 1300 to 2550 F. for a time. within the range of about one-quarter hour to aboutten hours to cause diffusion of the chromium into the surface of said titanium member.

9. A'me'thod of forming a hard surface layer on a titanium member which comprises applying thereto a mixture of a volatile organic vehicle and manganese powder, heating the titaniumrand manganese in an inert atmosphere at a temperature within the range of about 1410 F. to 1750 F. for a time within the range of about one-quarter hour to about ten hours to cause diffusion of the manganese into the surfaceof said titanium member, and thereafter reheating the treated member to a temperature of about 1700 F. and rapidly cooling the same.

10. A method as in claim 9 in which the cooled member is reheated to a temperature of about 500 F.

11. An articlecomposedof a titanium base member having a hard surface zone including titanium and at least one metal selected. from the group consisting of nickel, manganese and chromium and alloys thereof diffused into said titanium base member at a temperature below the melting point of titanium and below any eutectic of titanium and said other metal.

l2. A method of forming a hard surface layer on a ti- 7 tanium member which comprises applying to the titanium member a mixture of a volatile organic vehicle and manganese powder, and thereafter heating the titanium and manganese in an argon atmosphere at a temperature within the range of about 1000 F. to 2200,F."for a time withinthe range of about Mr hour to 10 hours to cause diffusion of the metals.

13. An article comprising a titanium base having a hard surface zone including titanium and nickel diffused into the surface of said titanium base at a temperature below the melting point of titanium and below any eutectic of titanium and nickel.

14. An article'comprisiug a titanium base having a hard surfacezone including titanium and manganese diffused into thejsurface of said titanium base at a temperature below the-melting point of titanium and below any eutectic of titanium and manganese.

15. An article comprising a titanium base having a hard surface zone including titanium and chromium diffused into the surface of said titanium base at a temperature below the melting point of titanium and below any eutectic of titanium and chromium.

References Cited in the file of this'patent UNITED STATES PATENTS 986,504 Rossi Mar. 14, 1911 1,565,724 Fonda; Dec. 15, 1925 2,520,373 Price Aug. 29, 1950 2,622,043 Roush Dec. 16, 1952 2,633,628 Bartlett Apr. 7, 1953 2,674,542 Alexander, Apr. 6, 1954- FOREIGN PATENTS 633,701 Great Britain Dec. 19, 1949 

1. A METHOD OF FORMING A SURFACE LAYER ON A TITANIUM MEMBER WHICH COMPRISES APPLYING THERETO A THIN LAYER OF AT LEAST ONE METAL POWDER SELECTED FROM THE GROUP CONSISTING OF NICKEL, MANGANESE AND CHROMIUM AND ALLOYS THEREOF, AND THEREAFTER HEATING THE TITANIUM MEMBER AND METAL POWDER TO A TEMPERATURE BELOW THE MELTING POINT OF TITANIUM AND THE POWDERED METAL AND BELOW ANY EUTECTIC TEMPERATURE OF TITANIUM AND THE POWDERED METAL FOR A TIME SUFFICIENT TO CAUSE DIFFUSION OF THE METAL POWDER INTO THE SURFACE OF SAID TITANIUM MEMBER. 